This invention relates to the preparation of titanium dioxide, and more particularly, to a process for preparing nodular pigmentary titanium dioxide from titanium dioxide-bearing materials.
Titanium dioxide (TiO.sub.2) is a well known opacifying pigment useful in paint and coating compositions, in plastic materials and as a filler in paper and other materials. Various known processes for producing TiO.sub.2 include, for example, conventional processes commonly referred to as the "sulphate" process and the "chloride" process.
The "sulphate" process involves solubilizing the titanium values in low grade titanium ores, such as ilmenite or sorelslag, with concentrated sulfuric acid and meticulously removing ferrous sulfate formed in the process. This is followed by precipitation, washing and calcining to form pigmentary TiO.sub.2.
The "chloride" process involves volatilizing, as tetrahalide, the titanium values in high grade titanium ores, such as Australian rutile (containing about 95 percent TiO.sub.2) or highly beneficiated ilmenite. This is followed by purification and oxidation.
The sulphate and chloride processes are very complex and capital intensive which accounts for the relatively costly product of TiO.sub.2 pigment made by such processes. It is, therefore, desired to provide a simplified process, and relatively less expensive process for preparing a TiO.sub.2 pigment whereby the titanium values in titanium dioxide-bearing materials or ores are not solubilized or converted to a vaporizable liquid compound, but are separated, through solid-liquid reactions, from the ore's impurities and mechanically comminuted to pigmentary size.
It is further desired to provide a TiO.sub.2 pigment which is nodular in shape.